Hi Tim,
I'm diverging from the thread here, but would you please describe the
"scavenging oxygen problem" with barium sulphate for me please. I have often
noted a lower CO yield from BASO4 than from other standards - I wonder if
this relates to what you speak of? 
Cheers
Robert Van Hale

> -----Original Message-----
> From: Stable Isotope Geochemistry 
> [mailto:[log in to unmask]] On Behalf Of Tim Prokopiuk
> Sent: Thursday, 9 March 2006 11:20
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] TC/EA Furnace Rerevisited
> 
> Greetings again...
> 
> Thanks to all for the information (Marilyn, Jon, Wolfram) 
> concerning a dying TC/EA oven.  To clarify a little further 
> what we are observing:
> 
> In the glassy carbon reactor we have only run benzoic acid, 
> potassium nitrate and silver phosphate, so no divalent 
> cations that I know of have ever been loaded.  We ran into 
> the scavenging oxygen problem with the barium sulphate 
> standard and quickly stopped using it many months ago.  But 
> what is strange about our current situation is that we had 
> two runs silver phosphate that ran well, and now suddenly 
> silver phosphate won't run properly.  We've tried twice 
> repacking the column with fresh glassy carbon fragments, and 
> the reactor is quite new (maybe only a couple hundred samples 
> run through it before this occurred).  I initially had 
> thought of a spent column, or that maybe the packing wasn't 
> quite right (a gap in the glassy carbon fragments maybe), but 
> this does not seem to be the case.
> 
> When we run benzoic acid or KNO3 and plot signal intensity 
> vs. mass I get a straight line.  When I try to run AgPO4 and 
> plot this it looks like a shot gun blast.  The d18O values 
> that show the expected yields all look good, but those that 
> fall below are depleted, so I am definitely losing oxygen 
> somewhere.  Those values that are low show peak tailing (my 
> lost oxygen most likely): the sign of a spent reactor.  But 
> the very next sample or two might run perfectly with good 
> numbers...this does not sound like a spent reactor.
> 
> I did notice on my water reactor that the hot zone 
> discoloration is in a very narrow zone now...I think I recall 
> that earlier in the life of the furnace the hot zone on the 
> glassy carbon reactors was larger?
> 
> Another question: how many times are people reusing their 
> graphite crucibles?  We flame ours to clean out the silver 
> buildup and then reuse them.  Maybe after a few times they 
> become less reactive somehow??
> 
> Any other takers?
> 
> Tim Prokopiuk
> 
> 
> -------------------------------------------------
> Tim Prokopiuk
> B. Sc. Geology/Technician
> Saskatchewan Isotope Laboratory
> Room 241
> Department of Geological Sciences
> University of Saskatchewan
> 114 Science Place
> Saskatoon, Saskatchewan, Canada
> S7N 5E2
> Phone: (306) 966-5712
> Fax: (306) 966-8593
> Email: [log in to unmask]
>